broadcast transmitters were going solid-state in the 70s, at least on AM. a station I knew in northern North Dakota lost the filter choke in an old Continental using 4-400s, so they had a nasty hum for a year, unobtanium. I dropped in one day around 1978 when the noise cleared, and they had a new Gates up. banks of TO-3 transistor amps off the exciter, blow some, plug more in. believe it was rated 5KW, but they only had a kilowatt of cards in due to their license. all commercial transmitters are custom-order and built when ordered.